Question

Find the sum of first 30 positive integers divisible by 7

Answer 1

20 numbers divisible by 5 or 7 are

=5,7,10,14,15,20,21,25,28,30,35,40,42,45,49,50,55,56,60 and 63.

And their sum are

5+7+10+14+15+20+21+25+28+30+35+40+42+45+49+50+55+56+60+63

= 670

Answer 2

Answer:

First 30 +ve integers divisible by 7

= 7 , 14 , 21 , .......... , 210

a = 7 , d = 7 , l = 210

Now ,

S30 = n / 2 × (a + l)

= 30/2 × (7 + 210)

= 15 × 217

= 3255

Therefore , sum of 1st 30 +ve integers divisible by 7 is 3255 .

HOPE THIS HELPS YOU .